Heap Webhooks API
Partner-registered webhook endpoints invoked by Heap. The only documented action type is `segment.users.sync`, which delivers delta adds/removes for a Heap behavioral segment. Signature verification: 1. Parse the `Heap-Hash` header (comma-separated key:value pairs). 2. Confirm the `ts` value is within the partner's tolerance window. 3. Concatenate `${ts}${requestbody}`. 4. Compute HMAC-SHA256 using the `webhook_secret_key` assigned at webhook creation. 5. Constant-time compare against the `hmac` value from the header. Return `200 OK` on success; `429` or other non-2xx responses trigger retries by Heap.